1. Field of the Invention
The present invention generally relates to a centrifugal fan and, more particularly, to a centrifugal fan capable of providing an improved cooling effect with reduced noise.
2. Description of the Related Art
FIG. 1 shows a conventional centrifugal fan 9 disclosed by Taiwan Patent No. M250230 entitled “A WIND-REDUCING RING STRUCTURE OF A CENTRIFUGAL FAN”. Centrifugal fan 9 includes a housing 91, an impeller 92 and a wind-reducing ring 93. Housing 91 includes an air inlet 911 and an air outlet. Impeller 92 is mounted in housing 91. A plurality of blades 921 is arranged on an outer peripheral wall of impeller 92. Wind-reducing ring 93 is coupled with an edge of each blade 921 that is adjacent to air inlet 911, so that the cooling effect of fan 9 can be improved.
Wind-reducing ring 93 of fan 9 may be arranged in a location which is just outside of a radial extent of air inlet 911 under an upper wall 91a of housing 91, as shown in FIG. 1. Alternatively, wind-reducing ring 93 may also be arranged in a location which is within the radial extent of air inlet 911 and is adjacent to upper wall 91a of housing 91, as shown in FIG. 2. However, in the arrangement shown in FIG. 2, upper edge 921a of each blade 921 is too close to upper wall 91a of housing 91. As such, upper edge 921a of blade 921 is liable to make contact with upper wall 91a of housing 91 during the rotation of impeller 92. In addition, due to the small distance between upper edge 921a of blade 921 and upper wall 91a of housing 91, wind noise easily results when impeller 92 draws air into fan 9 via air inlet 911.